Single-phase rectifiers, for example, such as ac-to-dc converters, with power factor correction or PFC providing power up to approximately 100 W are widely used as chargers for mobile devices or dedicated supplies. Common applications for such PFC rectifiers include, for example, personal computers, consumer electronics, telecommunication devices, and avionics equipment.
Increasingly, in addition to requiring a close to unity power factor (PF) and low total harmonic distortion (THD), emerging standards and applications are calling for PFC rectifiers with a programmable output voltage. For example, the IEEE Universal Power Adapter for Mobile Devices (UPAMD) standard, which defines a connection between a charger (adapter) and supplied mobile device, defines a communication link that sets up required output voltage level as well as voltage transition times. As another example, in an adaptive voltage bus system, a programmable dc bus voltage may be changed quickly based on the bad requirements.
Conventional PFC rectifier designs providing constant output voltage are not well suited for the emerging applications for programmable outputs. This is mostly due to a requirement for a large increase in the size/volume of the reactive components and or significant degradation in power processing efficiency of such emerging applications.
For conventional, constant output applications, a number of prior single-phase ac-dc solutions with power factor correction, have been proposed. Generally, these proposals can be divided into single and two-stage systems. In a typical low power application, where cost is a dominant factor, single stage solutions employing a flyback converter are frequently used. This is mostly due to the controller and system simplicity, and may also be due to the existence of galvanic isolation. However, these systems usually suffer from voltage regulation problems and require a bulky output capacitor to compensate for frequency line harmonics in the output voltage. Using as conventional design, the requirement for a variable and tight regulated output voltage necessitates a storage capacitor that is much larger, and therefore necessarily increases the requirement for its size. For example, to reduce the voltage from commonly used 20V down to 5V maintaining the same output voltage regulation (i.e. the ratio between the ripple and the desired output voltage value), a 16× larger capacitor is required. Such a capacitor would be by far the largest and most expensive component of the system, drastically increasing the overall volume and price of the PFC rectifier.
More complex two-stage solutions have better voltage regulation. In a two-stage solution, the first stage provides ac-dc rectification, and the second stage provides a dc-dc step-down which keeps the output voltage well regulated. In such two-stage systems, the intermediate voltage between the two stages is usually selected based on output voltage and there are design tradeoffs between the converter efficiency and dynamic response. In general, by reducing the difference between the input and output voltages, the efficiency of the downstream stage can be improved.
However, this improvement generally comes at the expense of a large increase in the energy storage capacitor (i.e. the intermediate capacitor value). This increase in the intermediate capacitor value comes from a hold-up time requirement, where the intermediate capacitor is required to provide energy for the supplied load during short input line voltage interruption periods. Since the value of the energy stored in a capacitor is proportional to the square of its voltage, each reduction of the capacitor voltage again requires an exponential increase in the capacitance value to maintain the same amount of energy (i.e. the same hold up time). As well, the reduced voltage degrades the dynamic response and, consequently, necessitates a larger capacitance value in the downstream converter. Both of these are serious concerns as they effect performance and cost.
These various limitations in prior PFC rectifier designs pose significant challenges. What is therefore needed is an improved PFC rectifier design which overcomes at least some of these limitations.
There area number of publications that discuss the prior art PFC rectifier designs, including the following:    [1] Universal Power Adapter for Mobile Devices, “IEEE UPAMD.” Internet: http://grouper.ieee.org/groups/msc/upamd, Jun. 19, 2010 [Jul. 18, 2011].    [2] K. Lee, F. C. Lee, J. Wei, and M. Xu, “Analysis and design of adaptive bus voltage positioning system for two-stage voltage regulators,” IEEE Transactions on Power Electronics, vol. 24, no. 12, pp. 2735-2745, August 2009.    [3] W. F. Ray, and R. M. Davis. “The definition and importance of power factor for power electronic converters,” in Proc. European conference on Power Electronics and Application's, EPE-1989, pp. 799-805, 1989.    [4] L. Huber, J. Zhang, M. M. Jovanovic, and F. C. Lee, “Generalized topologies of “Single-stage input-current-shaping circuits,” IEEE Trans., Power Electron., vol. 16, pp. 508-513, July 2001.    [5] R. Redl, L. Balogh, and N. O. Sokal. “A new family of single-stage isolated power-factor correctors with fast regulation of the output voltage,” in IEEE Power Electronics Specialists Conf., PESC-1994, pp. 1137-1144.    [6] R. Erickson, M. Madigan, and S. Singer. “Design of a simple high power factor rectifier based on the flyback converter,” in Proc. IEEE Applied Power Electronics Conf., APEC-1990, pp. 792-801.    [7] G. Choe, and M. Park, “Analysis and control of active power filter with optimized injection,” in Proc. IEEE Power Electronics Specialists Conference, PESC-1986, pp. 401-409.    [8] N. P. Papanikolaou, E. J. Rikos, and E. C. Tatakis, “Novel technique for high power factor correction in flyback converters,” in Proc. IEEE Electric Power Applications, vol. 148, no. 2, pp. 177-186, March 2001.    [9] W. Tang, V. Jiang G. C. Hue, F. C. Lee, and I. Cohen, “Power factor correction with flyback converter employing charge control,” in Proc. IEEE Applied Power Electronics Conference, APEC-1993, pp. 293-298.    [10] H. Wei, I. Batarseh. “Comparision of basic converter topologies for power factor correction,” in Proc. Southeastcon-1998, pp. 348-353.    [11] R. Oruganti, and M. Palanipan, “Inductor voltage control of back-type single-phase AC-DC converter,” IEEE Trans on Power Electronics, vol. 15, No, 2, pp. 411-417, March 2000.    [12] J. Zhang, M. M. Jovanovic, and F. C. Lee. “Comparison between CCM single-stage and two-stage boost converter,” in Proc. IEEE Applied Power Electronics Conference, APEC-1999, pp. 335-341.    [13] A. K. Jha, K. H. Babu, and B. M. Karan, “Parallel power flow AC/DC converter with high input power factor and tight output voltage regulation for universal voltage application,” in Proc. Power Electronics, Drives and Energy Systems, PEDES-2006, pp. 1-7.    [14] A. Pothana, and K. Vasudevan, “Parallel operation of power factor corrected AC-DC converter modules with two power stages,” in Proc. Conference on Power Electronics and Drive Systems, PEDs-2007, pp. 953-960.    [15] G. Spiazzi, S. Buso, and D. Tagliavia, “A low-loss high-power-factor flyback rectifier suitable for smart powerintegration,” in Proc. IEEE Power Electronics Specialists Conference, PESC-2000, vol. 2, pp. 805-810, 2000.    [16] J. A. A. Qahoug, G. Muralidhar. “Control scheme for high-efficiency high-performance two-stage power converters,” in Proc. Applied Power Electronics Conference end Exposition, APEC-2009, pp. 1226-1232.    [17] A. Radic, Z. Lukic, A. Prodic, and R. de Nie, “Minimum deviation digital controller IC for single and two phase dc-dc switch-mode power supplies,” in proc. IEEE Applied power Electronics Conference and Exposition (APEC), pp. 1-6, 2010.    [18] S. M. Ahsenuzzaman, A. Radi{grave over (c)}, and A. Prodić, “Adaptive switching frequency scaling digital controller for improving efficiency of battery powered dc-dc converters,” IEEE Applied Power Electronics Conference, APEC-2011, pp. 910-915, 2011.    [19] R. W. Erickson and D. Maksimovi{grave over (c)}, “Fundamentals of Power Electronics”, Second Edition, New York: Springer Science+Business Media, 2001.    [20] Lukic, Z. Zhao, S. M. Ansanuzzaman, and A. Prodic, “Self-tuning digital current estimator for low-power switching converters,” in IEEE Applied Power Electronics Conference (APEC-2008), pp. 529-534, March 2008.    [21] T.-L. Chern, L-H. Liu, C.-N. Huang, Y-L. Chern, and J. H. Kuang. “High power factor flyback converter for LED driver with boundary conduction mode control,” in Proc. IEEE Conference on Industrial Electronics and Applications, pp. 2088-2093, 2010,    [22] D. Maksimovi{grave over (c)}, and R. Erickson, “Modeling of cross-regulation in multiple-output flyback converters,” in IEEE Applied Power Electronics Confererence (APEC-1999), pp. 1068-1072, March 1999.    [23] Johns and K. Marlin, Analog Integrated Circuit Design, John Wiley & Sons, 1997.    [24] “AN10868, GreenChip TEA1733 series fixed frequency flyback controller,” Datasheet, NXP Semiconductor, 2010, available http://www.nxp.com.